CVE-2026-43160 Overview
CVE-2026-43160 affects the Linux kernel's mfd/macsmc driver, which provides System Management Controller (SMC) support for Apple Silicon Mac systems. The vulnerability stems from an uninitialized mutex in the struct apple_smc structure. The apple_smc_probe() function failed to initialize the mutex before sub-device probe functions invoked apple_smc_read(). Using an uninitialized mutex caused occasional NULL pointer dereferences during driver initialization. The fix initializes the mutex in apple_smc_probe() before any sub-device interactions occur.
Critical Impact
Uninitialized mutex use in the macsmc driver triggers NULL pointer dereferences during kernel driver probe operations on Apple Silicon hardware, potentially causing kernel crashes and denial of service.
Affected Products
- Linux kernel versions containing the mfd: macsmc driver prior to the patch
- Apple Silicon Mac systems running affected Linux kernel builds
- Distributions packaging vulnerable kernel revisions for Apple SoC platforms
Discovery Timeline
- 2026-05-06 - CVE-2026-43160 published to NVD
- 2026-05-06 - Last updated in NVD database
Technical Details for CVE-2026-43160
Vulnerability Analysis
The vulnerability resides in the Multi-Function Device (MFD) subsystem driver macsmc, which interfaces with the Apple System Management Controller on Apple Silicon hardware. The apple_smc_probe() function instantiates a struct apple_smc and registers sub-devices through the MFD framework. Sub-device probe routines call apple_smc_read() to query the controller during their own initialization.
The apple_smc_read() path acquires a mutex contained in the apple_smc structure to serialize access to the SMC. Because the mutex was never initialized via mutex_init() before sub-device probes ran, the locking primitives operated on zeroed or undefined state. This produced occasional NULL pointer dereferences rather than deterministic crashes, indicating a race-sensitive failure mode.
The upstream fix adds the missing mutex_init() call inside apple_smc_probe() prior to MFD child registration. This ensures the mutex is fully constructed before any consumer accesses it.
Root Cause
The root cause is a missing initialization step: the driver author allocated the apple_smc structure but omitted the call to mutex_init() for its embedded mutex. The result is classified as an Uninitialized Memory Use defect affecting a synchronization primitive [CWE-908]. Linux mutexes require explicit runtime initialization before lock or unlock operations.
Attack Vector
This defect triggers during normal kernel boot or driver load on Apple Silicon platforms. It is not a remotely exploitable flaw and does not appear to provide an attacker-controlled primitive. The practical impact is reliability and availability: the kernel may crash during early device initialization. No public exploit exists, and the EPSS data indicates negligible exploitation likelihood.
No synthetic exploitation code is provided. Refer to the upstream commits for the precise patch hunks: Kernel Git Commit 2d59325, Kernel Git Commit 414f65d, and Kernel Git Commit a1e9e29.
Detection Methods for CVE-2026-43160
Indicators of Compromise
- Kernel oops or panic messages referencing apple_smc_read or apple_smc_probe in dmesg and /var/log/kern.log.
- NULL pointer dereference traces originating from MFD sub-device probe functions on Apple Silicon hardware.
- Repeated boot failures or device initialization errors on Asahi Linux or similar distributions targeting Apple SoCs.
Detection Strategies
- Inventory running kernel versions across Linux fleets and flag builds that include the unpatched drivers/mfd/macsmc source.
- Compare installed kernel commit hashes against the fixed commits 2d59325, 414f65d, and a1e9e29 in the stable tree.
- Parse boot logs for stack traces involving SMC sub-device probes to identify systems experiencing the defect.
Monitoring Recommendations
- Forward kernel ring buffer events to a centralized log platform and alert on NULL pointer dereference signatures.
- Track unexpected reboots or boot loops on Apple Silicon Linux deployments and correlate with kernel version metadata.
- Subscribe to Linux stable tree announcements to receive timely notice of follow-up fixes for the macsmc driver.
How to Mitigate CVE-2026-43160
Immediate Actions Required
- Update affected systems to a Linux kernel version that includes the upstream fix initializing the apple_smc mutex in apple_smc_probe().
- Rebuild custom kernels by cherry-picking the fixed commits into the local tree before deployment to Apple Silicon devices.
- Validate that distribution-supplied kernel packages explicitly reference the patched commits in their changelog.
Patch Information
The fix is available in the Linux stable tree across the commits 2d5932588f029f7787f52c29174fead9bbc6b2cf, 414f65d6736342c77d4ec5e7373039f4a09250dd, and a1e9e299c0d9ea42ab1067b39fb72e976d3f1bdb. The patch adds mutex_init() to apple_smc_probe() so the lock is fully initialized before any sub-device probe consumes it.
Workarounds
- If patching is not immediately feasible, avoid loading the macsmc driver on affected Apple Silicon Linux systems by blacklisting the module.
- Defer Linux deployments on Apple Silicon hardware until a patched kernel is available from the distribution maintainer.
- Maintain console access and serial logging on affected hosts to capture diagnostic data if probe-time crashes occur.
# Verify installed kernel and confirm macsmc patch presence
uname -r
modinfo macsmc 2>/dev/null | grep -E 'filename|version'
# Optional: blacklist the driver until patched kernel is deployed
echo 'blacklist macsmc' | sudo tee /etc/modprobe.d/cve-2026-43160.conf
sudo update-initramfs -u
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
